The proposal has two broad goals: (1) to study and elucidate the specific interactions of p53 and human HMG-I(Y) on synthetic junction DNA and the possibility that the proteins interact; and (2) to study the chromatin structure of the p53 promoter in vitro and in vivo and the effects of HMG-I(Y) binding on chromatin structure. The first includes determining whether binding of these proteins to four-way junctions is mutually exclusive and identifying the binding sites of these proteins at base-pair resolution. The second will examine the effect of HMG-I(Y) on the p53 promoter chromatin structure in vitro and in vivo. Additionally, specific HMG-I(Y)-p53 protein-protein interactions will be identified by chemical crosslinking studies and antibody detection methods. Synthetic four-way junctions, p53 consensus sites, and the p53 promoter region will be used as DNA substrates. These experiments will include hydroxyl radical footprinting, electrophoretic mobility, reporter gene expression, and photocrosslinking techniques.